1. Field of the Invention
The present invention relates to a waveform synthesizing apparatus which synthesizes waveform data read from plural waveform memories so as to generate a musical tone signal.
2. Prior Art
In the conventionally developed electronic musical instrument, waveform data picked up from a non-electronic musical instrument and the like are stored in a waveform memory for a predetermined period and then such waveform data are read out so as to generate the musical tone. Fundamentally, such electronic musical instrument provides one waveform memory for one tone color so that the waveform data is read out in response to the period corresponding to the pitch of the operated key. In most of the non-electronic musical instruments, a slightly different waveform is picked up with respect to each of the higher tone area, middle tone area and lower tone area or with respect to each tone volume. For this reason, if the musical tone is formed by use of the same waveform data, the musical tone must be heard un-naturally and monotonously. Thus, another electronic musical instrument has been developed which provides plural waveform memories each storing different waveform data with respect to each tone area or each tone volume as shown in FIG. 1.
In FIG. 1, the whole tone area of a keyboard 1 is divided into several small tone areas each corresponding to the predetermined number of keys. Then, there are provided five waveform memories M0, M1, M2, M3, M4 each storing a different waveform, wherein each small tone area is assigned to each waveform memory. In each small tone area, the musical tone is to be formed based on the different waveform data stored in each waveform memory. When setting plural tone colors, the memory construction as shown in FIG. 1 is provided with respect to each tone color. In this case, the number of waveform memories may be different among some tone colors.
Meanwhile, there is a problem in that sounds of the electronic musical instrument as shown in FIG. 1 may be heard un-naturally because the waveform is changed remarkably between two keys corresponding to different tone areas respectively. In order to avoid such problem, the waveform data stored in two neighboring waveform memories are mixed together according to needs, so that the waveform is naturally varied at the boundary between the two neighboring tone areas in response to the change of tone area to be used.
In the case of the piano, the waveform must differ for each string-striking intensity. Thus, the electronic musical instrument capable of generating piano sounds provides plural waveform memories each corresponding to each of the touch intensities to be applied to the keys.
In order to obtain the delicate variation of the waveforms to be generated with respect to certain tone areas (e.g., higher tone area or lower tone area) of the keyboard, the number of waveform memories to be assigned to a certain tone area is set larger than that of the waveform memories to be assigned to other tone areas. In addition, once the above-mentioned keyboard characteristic is set, such keyboard characteristic is maintained even if the number of waveform memories is changed when changing over the tone color. That is because there is a tendency for the performer to play keyboard in consideration of its keyboard characteristic. Therefore, if the keyboard characteristic is changed in response to the change-over of the tone color, the expected performance effect cannot be obtained.
However, in the conventional electronic musical instrument, the waveform memory assignment is determined in advance in accordance with the number of waveform memories to be provided. Thus, there is a problem in that if the tone color is changed over, the waveform variation characteristic to be set to the keyboard must be varied, regardless of the performer's expectation.